Many people suffer physically and psychologically from the loss of their teeth. To aid such patients, it is known in the prior art to support a denture on a bone tissue-integrated (i.e., "osseointegrated") implant. Typically, the denture is attached to a cast member which is removably secured to the implant following osseointegration and healing.
Four factors typically affect the success of the prosthesis: patient selection, fixture design and manufacture, surgical technique, and prosthetic technique. Over the last several decades, there has been considerable increase in the success rates associated with tissue-integrated implants due primarily to material advancements and improved surgical techniques. While the current success rates are impressive, there have been few improvements in the techniques used to manufacture and install the prosthesis. This fact is surprising because the prosthetic procedures are crucial to the long-term success of the tissue-integrated implant. Such procedures, however, have not changed fundamentally from techniques used to restore teeth.
To insure a successful result during installation of the prosthesis, the prosthodontist must avoid premature loading, use good bridge design, and work with great accuracy. An ideal implant-supported prosthesis would be a single unit span over all implant abutments, and would reduce the distance opposing forces between abutments could act to approximately one micrometer. Due to the properties of the materials involved, indirect laboratory techniques are not capable of constructing a large cast framework for the prosthesis to this degree of accuracy. When the resulting framework is then fitted on the implant abutments, excessive stress may be present in the system, especially at the points where the coping screws attach the cast framework to the abutments. When excessive forces are then applied to the system, the coping screws may fail or rotate from their seatings. Such imperfect adaptation may allow microscopic flexure to occur, eventual fracture of the framework, or pressure-induced resorption of the bone around the implant.
Prior attempts at reducing stress have involved sectioning the framework into one or more sections and then soldering the sections together. While soldering at one or more points may result in a stable framework, this technique has not overcome the problems of the prior art because stress will not be evenly distributed among the abutments. Moreover, soldering is an indirect procedure subject to inaccuracies, is difficult, and requires an extra appointment for the patient.
There is therefore a need for an improved framework for an osseointegrated implant which overcomes these and other problems associated with prior art techniques.